The present invention relates to a method of monitoring a flexible pipe for transporting, over long distances, a fluid that is under pressure and possibly at a high temperature, such as a gas, oil, water or other fluids. The invention relates more particularly to the monitoring and warning of problems associated with a fracture of the armor wires of the flexible pipe in the vicinity of or inside the terminal end-fitting, where they are anchored, especially in a terminal end-fitting for a rising flexible pipe, called a “riser”, intended for offshore oil production. The present invention also relates to a device associated with the monitoring method.
Flexible pipes used offshore have various configurations depending on their precise use, but in general they satisfy the constructional criteria defined in particular in the API 17 B and API 17 J standards drawn up by the American Petroleum Institute under the title “Recommended Practice for Flexible Pipe” and “Specification for Unbonded Flexible Pipe”. These pipes comprise, from the inside outward:
an internal sealing sheath or pressure sheath, made of a plastic, generally a polymer, resistant to the chemical action of the fluid to be transported;
optionally, a pressure vault resistant mainly to the pressure developed by the fluid in the sealing sheath and consisting of the winding of one or more interlocked metal profiled wires, which may or may not be self-interlockable, that are wound in a helix with a short pitch (i.e. with a lay angle of close to 90°) around the internal sheath; the profiled wires have a cross section in the form of a Z or a T or their derivatives (teta® or zeta), or in the form of a U or an I; the said pressure vault may also include a hoop;
at least one ply (and generally at least two crossed plies) of tensile armor plies wound with a long pitch, the lay angle measured along the longitudinal axis of the pipe being less than 60°; and
an external protective sealing sheath made of a polymer.
Such a pipe may have a smooth internal bore, when the bore is formed directly by the sealing sheath (the pipe is then called a smooth bore pipe) or may have a rough bore, when a carcass consisting, for example, of an interlocked metal strip serving to prevent the pipe from collapsing under the external pressure is furthermore provided inside the internal sealing sheath.
The end-fittings for the pipes, which are intended for connecting them together or to terminal equipment, are also defined in the API 17 J recommendations and must be produced under conditions ensuring both good fastening and good sealing. They are generally obtained by crimping the sheath, that is to say by the partial radial penetration of a rigid element into the sheath.
Several types of end-fittings for flexible pipes using the principle of crimping the internal sheath are known, especially from documents FR 2 214 852 or WO 99/19655, or else from document WO 97/25564 in the name of the Assignee hereof, and document PCT/FR01/03305 also in the name of the Assignee. The latter document describes in particular a fastening end-fitting for a flexible tubular pipe, comprising a first annular portion (generally called the vault of the end-fitting) to which may bear a first crimping flange provided with a cone for crimping the internal sheath and a second annular portion (generally called a cap) which surrounds, and extends rearwards, the first annular portion and on which a second crimping flange can bear. The second crimping flange is provided with a cone for crimping the external sheath, cooperating with a rear crimping support sleeve. The second annular portion defines with the first annular portion an annular space in which the tensile armor plies are placed in such a way that they are radially separate from the internal sheath so as to pass around the first crimping flange and the first annular portion in order to be fastened thereto. The end-fitting includes a collar for immobilizing the armor wires between the first crimping flange and the second crimping flange. The aforementioned annular space is intended to be filled with a filling material such as a resin which will immobilize the various elements lying in this space.
It is known to monitor the integrity of a pipe and a pipe end-fitting over time using various methods and devices for the purpose of detecting certain anomalies.
Thus, methods are known for inspecting the inside of a pipe, using an inspection “pig” traveling along the pipe and giving, for example, video images or identifying a possible retraction of the carcass at an end-fitting by an eddy current system and associated sensors (see FR 2 790 087 in the name of the Assignee). Besides the fact that such methods give information about the carcass but not directly about the sheath (in the case of rough bore pipes), they have a drawback of requiring production to be temporarily stopped in order to send the pig into the pipe.
Methods are also known for detecting leaks in pipes (FR 2 626 974 and U.S. Pat. No. 4,775,855) or for detecting the imminent fracture of a pipe using sensor elements placed on the pipe (GB 2 057 696).
Methods have also been developed that are more specifically associated with the monitoring of end-fittings because it has been noted that these are the site of certain types of deterioration over time. It is useful to be able to detect in time such deterioration in order to be able to intervene in a programmed manner on the pipe and on the end-fitting, and to carry out the necessary repairs or replacements.
In particular, it is known and recommended to monitor the position of the pressure sheath by regular inspection.
To be able to obtain sheath displacement information effectively, it has been proposed in document WO 98/12545 to provide markers on the element to be monitored, the displacement of which markers can be detected by X-rays using an X-ray detector or an X-ray sensitive photographic film. In all cases, this requires heavy equipment and also requires production to be stopped in order to be able to place the detector around the pipe.
The Assignee has also proposed, in French application No. 02/02155, a detection method and an associated end-fitting that can provide information about the displacement of the pressure sheath or of other layers of the pipe without having to stop production. The end-fitting is suitable for detection, because it is equipped directly with a sensor for detecting the displacement of a given layer in the pipe, especially the pressure sheath.
Document U.S. Pat. No. 3,972,223 relates to a method and to a device for monitoring the integrity of a pipe over its length or over the length of each of its sections. The document provides for elongate bladders to be placed in the thickness of the multilayer wall of the pipe, said bladders being filled with a pressurized fluid and communicating via tubes with one or more pressure gauges. Any impact along the length of the pipe, or destruction of the layers of the wall of the pipe, results in variations of the pressure of the fluid contained in the bladders, these being detected by the pressure gauge or gauges. However, that document does not in any way show that this method can be used for monitoring the end-fittings themselves.
Document GB 2 148 447 shows a connection end-fitting. An annular space lying between two armor plies experiences its pressure measured using a pressure gauge, to which the annular space is connected via a bore. This pressure gauge can detect anomalies in the leakage rate that may indicate damage of the armor plies, this damage not necessarily being located in the end-fitting. That document therefore does not teach monitoring in the terminal end-fitting either.
All these monitoring methods help as far as possible to prevent production incidents in the pipe. However, in certain causes of impairment to the flexible pipe the end-fitting cannot be detected by the existing method. This is especially the case as regards the fracture of certain of the wires forming the tensile armor plies. Such fracture of the wires, which is progressive over time, may result in destruction of the end-fitting and therefore of the pipe when the number of wires damaged increases. Thus, the present invention is aimed at improving the monitoring of the terminal end-fittings of flexible pipes so as to prevent sudden production stoppages. It essentially consists in monitoring, and giving warning about, potential incidents relating to the integrity of the wires of the tensile armor plies inside the end-fitting.